The inventive impact-modified polycarbonate (PC) compositions are characterized by their excellent low temperature ductility, and improved processing properties expressed by relatively high melt fluidity during injection molding. The inventive compositions have good processing stability at high temperatures, good stability to ageing under damp heat conditions and a good resistance to stress-cracking. An embodiment of the invention relates to flame-resistant compositions which, with a high ductility, are distinguished by improved processing properties characterized by a relatively high melt fluidity during injection molding.
Impact-modified polycarbonate compositions, e.g. those blends with ABS (acrylonitrile/butadiene/styrene), are known for their high ductility at room temperature and low temperatures and good processing properties. However, for realization of demanding uses, in particular complex component geometries, it is often desirable to improve the processing properties further. Conventional measures lead to the desired improvement, however, as a rule cause a deterioration in the toughness and/or resistance to stress-cracking under the influence of media such as solvents, oils, fats etc. This is critical inasmuch as high quality requirements of ductility, in some cases down to low temperatures, are as a rule imposed on components of PC/ABS, e.g. safety parts in automobile construction. In this as also other fields of use of PC/ABS blends, such as, for example, in the case of housing for electronic equipment, the materials often also come into contact with various media (e.g. fats, oils, solvents, skin creams etc.) and should withstand such media influences undamaged for as long as possible, including under mechanical stress.
A further requirement of PC/ABS compositions is an improved processing stability as well as stability to hydrolysis, i.e. long-term stability in a damp heat climate. This is necessary in order to ensure that the mechanical properties are realized at a high level over a wide processing window and are subject to as few changes as possible, including after storage under hot or hot damp conditions.
WO 01/25334 discloses that PC/ABS compositions based on ABS which has been prepared in the bulk polymerization process have good processing stability as well as an improved balance of low temperature toughness and melt flowability. EP 0 900 827 disclosed that PC/ABS compositions based on ABS which has been prepared in the emulsion polymerization process also have good processing stability if the impact modifier prepared in the emulsion process is substantially free from basic components and has been prepared on the basis of specific emulsifiers, such as alkylsulfonates. WO 91/18052 A1 discloses PC/ABS compositions of high heat stability, which are characterized in that the graft polymers have a sodium ion and potassium ion content of less than 1,500 ppm, preferably less than 800 ppm, and comprise a certain amount of antioxidants. WO 99/11713 A1 discloses flameproofed PC/ABS compositions having an improved resistance to moisture and at the same time a high level of mechanical properties, which are characterized in that the graft polymers have a content of alkali metals of less than 1 ppm. In particular, the sodium ion and potassium ion content of the graft polymer should be less than 1 ppm.
Such PC/ABS compositions which comprise a mixture of various ABS graft polymers prepared by different polymerization processes are also known.
U.S. Pat. No. 4,624,986 and U.S. Pat. No. 4,526,926 disclose low gloss compositions containing polycarbonate and graft copolymer. The graft copolymer prepared by bulk polymerization process or by the emulsion polymerization process or mixtures thereof. No limitation is specified relative to molecular weight of the SAN in the ABS employed.
U.S. Pat. No. 4,677,162 discloses thermoplastic compositions which comprise aromatic polycarbonate, a graft copolymer of acrylonitrile/butadiene/styrene (ABS) and an impact modifier. The ABS graft polymer is prepared by the bulk polymerization process and has a polybutadiene content of from 1 to 18 wt. % and an average rubber particle size of greater than 0.75 μm. An elastomer-based graft copolymer preferably prepared by the emulsion process, the elastomer content of which is between 15 and 98 wt. % and the average rubber particle size of which is less than 0.75 μm, is disclosed as the impact modifier. The influence of the molecular weight of the SAN contained in the ABS is not discussed.
EP-A 0 312 929 discloses PC/ABS compositions with mixtures of at least two graft copolymers, the one graft copolymer having been prepared by the emulsion process and being present in excess, based on the total amount in the total elastomer content, and the other graft copolymer having been prepared by another process (e.g. bulk or bulk-suspension polymerization.
WO 94/24210 discloses thermoplastic compositions comprising aromatic polycarbonate, a mixture of at least two graft copolymers, the one graft copolymer having been prepared by the bulk polymerization process and the other graft copolymer having been prepared by the emulsion polymerization process, a copolymer containing epoxide groups and optionally an aromatic copolymer.
EP-A 0 456 030 discloses PC/ABS compositions comprising polycarbonate and a graft polymer component comprising a mixture of bulk graft polymer and emulsion graft polymer, the content of emulsion graft polymer in the graft polymer component being 10-50 wt. %.
EP 0 372 336 A2 discloses PC/ABS compositions having a high toughness at low temperatures, which are characterized in that the graft polymers and/or the copolymers are replaced at least in part by graft polymers and/or copolymers in which the graft base and/or the copolymer comprises at least 86 wt. % of vinylaromatics. Nothing is said about the molecular weights of SAN in the various graft polymers and copolymers.
WO 99/65991 discloses impact-modified polycarbonate compositions having improved galvanizing properties which comprise a mixture of two graft copolymers, the one graft polymer comprising free SAN copolymer having an average molecular weight of from 50,000 to 150,000 g/mol. The examples disclose compositions comprising a graft polymer mixture which differ in the average molecular weight of the free SAN copolymer contained in the particular graft polymer by up to 30,000 g/mol.
The object on which the invention is based is to provide PC/ABS molding compositions for the production of complex moldings which have an improved balance of toughness, including at low temperatures, and melt flowability and moreover have a good resistance to ageing under the influence of a damp heat climate, a good processing stability and a good resistance to chemicals. The object of the invention is furthermore to provide flame-resistant molding compositions of high toughness and improved melt flowability.